The present invention relates to a non-resonance type knock sensor for detecting knocks or vibrations caused in an internal combustion engine by means of a piezoelectric element that is held in a compressed state inside a housing.
There have been developed various knock sensors that are attached to internal combustion engines. One of them is a non-resonance type knock sensor that detects knocks caused in the internal combustion engine by means of a piezoelectric element held in a compressed state inside a housing and supplies a detection signal to the outside.
Generally, the non-resonance type knock sensor has a support member including a main body portion formed with a hole through which a bolt extends and a radially outward flange portion at one axial end of the main body portion. On the flange portion is placed a piezoelectric element and a weight in this order. The piezoelectric element and weight have holes through which the main body portion extends. Further, between the flange portion and the piezoelectric element is disposed an output terminal for supplying a detection signal produced by the piezoelectric element to the outside. In the meantime, in case the support member and the weight are formed of a conductor such as metal, insulation members are disposed on the outer circumferential periphery of the main body portion and the flange portion which the piezoelectric element and the output terminal are brought into contact with and between the weight and the output terminal, thereby preventing the flow of the detection current produced at the piezoelectric element to the support member and the weight.
Herein, the main body portion has at an outer circumferential section located above the weight a male thread section. The piezoelectric element and the weight are fixed together with the output terminal to the support member, in a state of being pressed with a predetermined force toward the flange portion by means of a washer and a nut. All of the constituent parts are encased in a housing made of a resinous material and thereby protected from an impact or the like force applied thereto from the outside.
The non-resonance type knock sensor structured as above is attached to a cylinder head of an internal combustion engine by means of a bolt extending through the hole formed in the main body portion of the support member. By this, the weight and the piezoelectric element constituting the non-resonance type knock sensor are caused to vibrate together with the internal combustion engine. As a result, a detection signal of the same waveform as that of vibrations caused in the internal combustion engine is supplied from the output terminal to the outside.
In the meantime, the detection signal is supplied from the output terminal through, for example, a band-pass filter that limits the frequencies of vibrations caused in the internal combustion engine to those within a passed frequency band, to an ECU (Engine Control Unit) where it is determined whether knocks are caused.